Current Emission Standards

Please note that some states have adopted emission standards set in place by the California Air Resources Board (CARB), including California and several northeastern states. As Texas uses the emission standards set in place by EPA, this information is limited to a discussion of these standards. For more information on the California emission standards, please visit CARB. Below are additional details on EPA standards for vehicles registered for on-road use.

The Environmental Protection Agency (EPA) first began setting emission standards for motor vehicles in the late 1960's. Since then, the standards have changed multiple times, becoming more strict as technology advanced and policymakers gained a greater understanding of how vehicle emissions impact the environment and human health. Emission standards are developed separately for different types of vehicles and can generally be organized into three different areas: light- and medium-duty vehicles, heavy-duty vehicles, and nonroad equipment (such as locomotives and construction equipment). For federal emission standards for all on-road and nonroad vehicles and engines, and related fuel sulfur standards, see the EPA Emission Standards Reference Guide.

Light-Duty and Medium-Duty Vehicles

Light-duty vehicles generally includes all vehicle types designated for passenger use that are less than 8,500 pounds gross vehicle weight, though a "medium-duty passenger vehicle" category includes vehicles between 8,500-10,000 pounds. For this vehicle category, EPA established the Tier 2 Vehicle and Gasoline Sulfur Program, which set rules in place that introduced two major elements for the first time. First, the vehicle and the fuel are treated as a single system. The rules therefore significantly reduced the sulfur content of gasoline, enhancing the effectiveness of modern emissions control technology in the vehicles themselves. Second, all passenger vehicles are now held to the same emissions standards, regardless of size or fuel type. The new emissions standards introduced in this program, commonly referred to as Tier 2 standards, phased in starting with model year 2004 and ending with model year 2009. These standards apply to all light-duty passenger vehicles and created a new class of automobiles called "medium-duty passenger vehicles" which encompasses the heavier sport utility vehicles and passenger trucks and vans that have a gross vehicle weight rating between 8,500 and 10,000 pounds.

Under the Tier 2 standards, passenger vehicles are certified to individual "bins", and each bin corresponds to a specific emission rate for each pollutant. The lower the Bin number, the cleaner the vehicle, with Bin 1 being equivalent to zero emissions. From 2004-2008, the bins ranged from Bin 1 to Bin 11. Bins 9-11 began phasing out in 2006 and expired for the heaviest vehicles in 2008, so the available vehicle certifications range from Bin 1 to Bin 8, beginning with model year 2009. Manufacturers must ensure that the vehicle fleets they produce average to a Tier 2 Bin 5 certification, which is equal to an emission rate of 0.07 grams per mile of nitrogen oxides (NOx). For comparison, a vehicle certified as a Low Emission Vehicle (LEV) under the National Low Emission Vehicle program, which was in place from 2001-2003, emitted NOx at a rate of 0.3 grams per mile.

FWTAier 2 Bin rating system applies to all passenger vehicles, regardless of fuel type. This enables consumers to directly compare the emissions of vehicles fueled by gasoline, diesel, and alternative fuels to one another, as they are all certified under the same system. The table below provides details on the specific emission rates of each Bin classification. For more information, visit the following links:

Emission Standard (in grams/mile, certified over full useful life of 100,000-120,000 miles)

Model Year

Bin Rating

Nitrogen Oxides (NOx)

Particulate Matter (PM)

Carbon Monoxide (CO)

Formaldehyde (HCHO)

2004+

Bin 1

0

0

0

0

2004+

Bin 2

0.02

0.01

2.1

0.004

2004+

Bin 3

0.03

0.01

2.1

0.011

2004+

Bin 4

0.04

0.01

2.1

0.011

2004+

Bin 5

0.07

0.01

4.2

0.018

2004+

Bin 6

0.1

0.01

4.2

0.018

2004+

Bin 7

0.15

0.02

4.2

0.018

2004+

Bin 8

0.2

0.02

4.2

0.018

2004-2008

Bin 9

0.3

0.06

4.2

0.018

2004-2008

Bin 10a

0.6

0.08

4.2

0.018

2004-2008

Bin 10b-10c

0.6

0.08

6.4

0.027

2004-2008

Bin 11

0.9

0.12

7.3

0.032

Note: Bins 9-11 expired in model year 2006 for cars and light-duty truck classes 1 and 2, and expired in model year 2008 for light-duty truck classes 3 and 4. Click here for details on the different types of vehicles.

Note: This table is intended to be used as a guide only. While every effort has been made to ensure accuracy, it is not a substitute for official regulations.

Heavy-Duty Vehicles

Heavy-duty vehicles are generally defined as those with a gross vehicle weight rating above 8,500 pounds, and include many different types of vehicles such as delivery trucks, buses, and tractor-trailers, or eighteen-wheelers. EPA adopted Tier 2 standards for heavy-duty on-road vehicles through the Heavy-Duty Engine and Vehicle Standards and Highway Diesel Fuel Sulfur Control Requirements, also known as the 2007 Heavy-Duty Highway Rule. This rule began to treat the engine and the fuel that goes into it as a single system and thus contained regulations reducing sulfur content in diesel fuel in addition to establishing new engine standards. Thus, the phase-in schedule of cleaner engines is directly correlated with the availability of cleaner diesel fuels. More information about diesel fuel regulations is available on the Clean Fuels page.

The new engine emission standards set forth by the 2007 Heavy-Duty Highway Rule also establish a uniform emission certification for all heavy-duty on-road engines, regardless of fuel type. This enables direct comparison of the cleanliness of different engines, as all are held to the same standard. New emission standards began to phase in with model year 2007 engines and must be fully implemented by 2010. Heavy-duty engine manufacturers began phasing in cleaner engines at different rates, so much variability in emission rates exists among newer heavy-duty engines, starting with engines manufactured in 2004.

The 2007 Heavy-Duty Highway Rule resulted in two major benchmarks for the heavy-duty vehicle industry: one in 2007 and one in 2010. In 2007, strict particulate matter (PM) emissions standards came into effect that required the use of both cleaner engines and ultra-low sulfur diesel (ULSD) fuel. Engine manufacturers integrated advanced emissions control technologies, such as diesel particulate filters and other devices that reduce PM, into newly built engines in order to meet compliance with the new engine standards. These emission control technologies cannot tolerate the higher sulfur content that had been in older diesel formulations, thus ULSD was required to be available across the refueling network in order to supply this new group of engines.

The year 2010 marks the deadline for phasing in a new emission standard for nitrogen oxides (NOx), which is the main pollutant of concern in the Dallas-Fort Worth ozone nonattainment area. By this year, engines must ultimately meet an emission standard of 0.2 grams of NOx per brakehorsepower-hour (g/bhp-hr). This deadline has great significance both for manufacturers and heavy-duty engine users, as the standard is very strict and has required the introduction of new technologies in engine production. Diesel engines will require the most innovation, as most manufacturers agree that additional exhaust aftertreatment will be necessary in order to create a "2010-compliant" diesel engine. The most likely technology to reduce NOx to the required level is selective catalytic reduction, or SCR, which utilizes a urea solution and may require investment in new storage and distribution infrastructure. Several engines using gasoline, natural gas, and propane have already been certified to the 0.2 g/bhp-hr standard. The table below outlines heavy-duty emission standards that have been phased in starting with the late 1990's.

Note: Many engines manufactured from 2003-2009 met a more stringent emission rate for NOx, but the Texas Commission on Environmental Quality assumes default emissions as shown above unless a certificate documenting a lower emission rate is produced.

Heavy-Duty Gasoline Engine Emission Standards

Model Year

Nitrogen Oxides (NOx)

Particulate Matter (PM)

Carbon Monoxide (CO)

NOx + Non-Methane Hydro-Carbons (NMHC)

NMHC

2008 +

0.2

0.01

14.4

-

0.14

2005-2007

-

-

37.1

1

-

1998-2004

4

-

37.1

-

-

Note: These table are intended to be used as guides only. While every effort has been made to ensure accuracy, they are not a substitute for official regulations.